1. Field of the Invention
This invention relates to a heater for heating a heat shrinkable tube fitted over a junction between optical fiber cables or electric cables.
2. Prior Art
FIG. 1 shows one conventional heater 100 of the type described which comprises a rectangular base 102, a pair of support members 104 and 104 fixedly mounted on a top surface of the base 102 at opposite ends thereof, a pair of parallel spaced shield plates 106 and 106 fixedly mounted on the top surface of the base 102 and disposed between the pair of support members 104 and 104, and three electric heating elements 108a, 108b and 108a disposed between the pair of shield plates 106 and 106 and spaced therealong. In operation, a heat shrinkable tube 110 is fitted over two optical fiber cables 112 and 112 to cover a junction 114 between their conductors 116 and 116. Then, the two optical fiber cables 112 and 112 are placed on the pair of support members 104 and 104 with the heat shrinkable tube 110 disposed above the three heating elements 108a, 108b and 108a. Then, the heating elements 108a, 108b and 108a are operated to heat the heat shrinkable tube 110 so that the tube 110 is shrunk radially inwardly to seal the joint 114. During this heating operation, if the opposite end portions of the heat shrinkable tube 110 are first shrunk, air is entrapped in the central portion of the tube 110 intermediate the opposite end portions. Such residual or entrapped air affects the reinforcement of the cable joint portion by the tube 110. Therefore, it is necessary to shrink the heat shrinkable tube 110 from the central portion toward the opposite end portions. One method is to heat the central heating element 108a at a temperature slightly higher than the temperature at which the other two heating elements 108a and 108a are heated. Another alternative is to first heat the central heating element 108b for a predetermined period of time to shrink the central portion of the tube 110 and then to start the heating of the other two heating elements 108a and 108a to shrink the opposite end portions of the tube 110. Thus, two kinds of heating elements to be operated at different heating temperatures are required for carrying out the former method. And, the latter method requires the three heating elements and a timer means for sequentially operating them in a manner described above. Therefore, the conventional heater is rather complicated in construction and expensive.